1. Field of the Invention
The present invention relates to a spin-valve thin-film element which causes a change in electrical resistance by the relationship between the direction of pinned magnetization of a pinned magnetic layer and the direction of variable magnetization of a free magnetic layer affected by an external magnetic field, and to a thin-film magnetic head provided with the spin-valve thin-film element. In particular, the present invention relates to a spin-valve thin-film element having a biasing conductive layer in which a current applied to the biasing conductive layer can control the variable magnetization direction of the free magnetic layer, and exhibiting high heat resistance and reliability and small asymmetry, and to a thin-film magnetic head provided with the spin-valve thin-film element.
2. Description of the Related Art
Spin-valve thin-film elements belong to giant magnetoresistive (GMR) elements and detect magnetic fields recorded on recording media such as hard disks. Among the GMR elements, the spin-valve thin-film elements have relatively simplified structures exhibit large rates of change in resistance in response to external magnetic fields, and are sensitive to weak magnetic fields. The spin-valve thin-film elements are classified into single spin-valve thin-film elements and dual spin-valve thin-film elements.
FIG. 21 is a cross-sectional view of a conventional spin-valve thin-film element viewed from an opposing face opposing a recording medium. This spin-valve thin-film element is of a bottom type including a pair of composites, each including an antiferromagnetic layer, a pinned magnetic layer, a nonmagnetic layer, and a free magnetic layer. In FIG. 21, the magnetic recording medium, such as a hard disk moves in the Z direction, and generates a fringing magnetic field in the Y direction.
An antiferromagnetic layer 20 composed of a NiO alloy, a FeMn alloy, or a NiMn alloy is formed on an underlying layer 10 composed of tantalum (Ta). A pinned magnetic layer 30 composed of cobalt (Co) or a NiFe alloy is formed on the antiferromagnetic layer 20. Since the pinned magnetic layer 30 is in contact with the antiferromagnetic layer 20, an exchange coupling magnetic field (an exchange anisotropic magnetic field) is generated between the pinned magnetic layer 30 and the antiferromagnetic layer 20 and the pinned magnetization of the pinned magnetic layer 30 is pinned, for example, in the Y direction in the drawing.
A nonmagnetic conductive layer 40 composed of copper (Cu) is formed on the pinned magnetic layer 30, and a free magnetic layer 50 composed of the same material as that of the pinned magnetic layer 30 is formed on the nonmagnetic conductive layer 40. The free magnetic layer 50 is covered with a protective layer 70 composed of Ta.
Hard biasing layers 60 composed of, for example, a cobalt-platinum (Coxe2x80x94Pt) alloy are formed on both sides of the composite from the underlying layer 10 to the protective layer 70. The hard biasing layers 60 are magnetized in the direction opposite to the X1 direction in the drawing so that the variable magnetization of the free magnetic layer 50 is oriented in the direction opposite to the X1 direction. Thus, the variable magnetization of the free magnetic layer 50 and the pinned magnetization of the pinned magnetic layer 30 are perpendicular to each other.
Conductive layers 80 composed of Cu or the like are formed on the hard biasing layers 60 and lead a detecting current to the pinned magnetic layer 30, the nonmagnetic conductive layer 40, and the free magnetic layer 50.
In this spin-valve thin-film element, the fringing magnetic field from the magnetic recording medium such as the hard disk changes a variable magnetization of the free magnetic layer 50 oriented in the direction opposite to the X1 direction. Such a change in the variable magnetization causes a change in electrical resistance of the spin-valve thin-film element in relation to the pinned magnetization of the pinned magnetic layer 30. As a result, the fringing magnetic field from the magnetic recording medium is detected as a change in voltage due to the change in the electrical resistance.
It is preferable in the spin-valve thin-film element that the variable magnetization of the free magnetic layer 50 and the pinned magnetization of the pinned magnetic layer 30 be close to 90 degrees in order to ensure high heat resistance, high reliability, and small symmetry. The direction of the variable magnetization of the free magnetic layer 50, however, is undesirably tilted from 90 degrees by a magnetostatic coupling magnetic field of the pinned magnetic layer 30 and a current magnetic field of the detecting current.
With reference to FIG. 22, when a magnetostatic coupling magnetic field Hp4 of the pinned magnetic layer 30 and a current magnetic field Hi4 of a detecting current i4 are formed in the same direction (assisting direction), the variable magnetization Hf10 of the free magnetic layer 50 is tilted as variable magnetization Hf11 towards a combined magnetization moment of the magnetostatic coupling magnetic field Hp4 and the current magnetic field Hi4.
With reference to FIG. 23, when a magnetostatic coupling magnetic field Hp5 of the pinned magnetic layer 30 and a current magnetic field Hi5 of a detecting current i5 are formed in different directions (counter directions) from each other and when the magnetostatic coupling magnetic field Hp5 is larger than the current magnetic field Hi5, a variable magnetization Hf20 of the free magnetic layer 50 is tilted as variable magnetization Hf21 towards the combined moment of the magnetostatic coupling magnetic field Hp5 and the current magnetic field Hi5, that is, in the direction of the magnetostatic coupling magnetic field Hp5.
With reference to FIG. 24, when a magnetostatic coupling magnetic field Hp6 of the pinned magnetic layer 30 and a current magnetic field Hi6 of a detecting current i6 are formed in different directions (counter directions) from each other and when the magnetostatic coupling magnetic field Hp6 is smaller than the current magnetic field Hi6, a variable magnetization Hf30 of the free magnetic layer 50 is tilted as variable magnetization Hf31 towards the combined moment of the magnetostatic coupling magnetic field Hp6 and the current magnetic field Hi6, that is, in the direction of the current magnetic field Hi6.
As shown in FIGS. 22 to 24, the tilt of the variable magnetization of the free magnetic layer 50 does not maintain a perpendicular relationship between the variable magnetization of the free magnetic layer 50 and the pinned magnetization of the pinned magnetic layer 30. Thus, heat resistance and reliability are deteriorated, and asymmetry is increased. Accordingly, this spin-valve thin-film element may erroneously process signals from the magnetic recording medium.
FIG. 25 is a cross-sectional view of another conventional spin-valve thin-film element viewed from an opposing face opposing a recording medium. This spin-valve thin-film element is of a dual type including a free magnetic layer and a pair of composites formed on both faces thereof, each including a nonmagnetic conductive layer, a pinned magnetic layer, and an antiferromagnetic layer.
This dual spin-valve thin-film element including two triple-layered composites, each including the free magnetic layer, the nonmagnetic conductive layer, and the pinned magnetic layer, exhibits a larger rate of change in resistance compared to the single spin-valve thin-film element shown in FIG. 21, and is advantageous considering trends toward high-density recording. In FIG. 25, the magnetic recording medium, such as a hard disk, moves in the Z direction and generates a fringing magnetic field in the Y direction.
In the dual spin-valve thin-film element, an underlying layer 41, an antiferromagnetic layer 42, a lower pinned magnetic layer 43, a nonmagnetic conductive layer 44, a free magnetic layer 45, a nonmagnetic conductive layer 46, an upper pinned magnetic layer 47, an antiferromagnetic layer 48, and a protective layer 49 are deposited in that order. Hard biasing layers 32 and conductive layers 33 are formed on both sides of the composite from the underlying layer 41 to the protective layer 49. These layers are substantially composed of the same materials as those of the single spin-valve thin-film element shown in FIG. 21.
Since the lower pinned magnetic layer 43 and the upper pinned magnetic layer 47 are in contact with the antiferromagnetic layer 42 and the antiferromagnetic layer 48, respectively, exchange coupling magnetic fields (exchange anisotropic magnetic fields) are generated between the lower pinned magnetic layer 43 and the antiferromagnetic layer 42 and between the upper pinned magnetic layer 47 and the antiferromagnetic layer 48. The pinned magnetization of the lower pinned magnetic layer 43 and the pinned magnetization of the upper pinned magnetic layer 47 are pinned, for example, in the Y direction in the drawing.
The hard biasing layers 32 are magnetized in the direction opposite to the X1 direction in the drawing so that the variable magnetization of the free magnetic layer 45 is oriented in the direction opposite to the X1 direction. Thus, the variable magnetization of the free magnetic layer 45 is perpendicular to both the pinned magnetization of the lower pinned magnetic layer 43 and the pinned magnetization of the upper pinned magnetic layer 47.
In this dual spin-valve thin-film element, the fringing magnetic field from the magnetic recording medium such as the hard disk changes a variable magnetization of the free magnetic layer 45 oriented in the direction opposite to the X1 direction. Such a change in the variable magnetization causes a change in electrical resistance of the spin-valve thin-film element in relation to the pinned magnetization of the lower pinned magnetic layer 43 and the pinned magnetization of the upper pinned magnetic layer 47. As a result, the fringing magnetic field from the magnetic recording medium is detected as a change in voltage due to the change in the electrical resistance.
It is preferable also in the spin-valve thin-film element that the variable magnetization of the free magnetic layer 45 and the pinned magnetization of the pinned magnetic layers 43 and 47 be close to 90 degrees in order to ensure high heat resistance, high reliability, and small asymmetry.
In the dual spin-valve thin-film element, as shown in FIG. 26, the direction of a variable magnetization Hf40 of the free magnetic layer 45 is undesirably tilted as a variable magnetization Hf41 towards magnetostatic coupling magnetic fields Hp40 and Hp50.
That is, current magnetic fields Hi40 and Hi50 of detecting currents i40 and i50 affect the variable magnetization Hf40 of the free magnetic layer 45 from opposite directions so that the influences are offset. Hence, the direction of the variable magnetization Hf40 of the free magnetic layer 45 is less affected. In contrast, the magnetostatic coupling magnetic fields Hp40 and Hp50 of the lower pinned magnetic layer 43 and the upper pinned magnetic layer 47 affect the variable magnetization Hf40 of the free magnetic layer 45 in the same direction, and thus affect the direction of the variable magnetization Hf40 of the free magnetic layer 45.
As a result, the direction of the variable magnetization Hf40 of the free magnetic layer 45 is tilted as the variable magnetization Hf41 towards combined magnetization moments of the current magnetic fields Hi40 and Hi50 of the magnetostatic coupling magnetic fields Hp40 and Hp50, that is, towards the direction of the current magnetic fields Hi40 and Hi50.
When the variable magnetization Hf41 of the free magnetic layer 45 is tilted, the variable magnetization Hf41 is not perpendicular to the pinned magnetization of the lower pinned magnetic layer 43 and the pinned magnetization of the upper pinned magnetic layer 47. Thus, also in the dual spin-valve thin-film element, heat resistance and reliability are deteriorated, and asymmetry is increased. Accordingly, this spin-valve thin-film element may also erroneously process signals from the magnetic recording medium.
A possible method to control the tilt of the variable magnetization of the free magnetic layer is to control the intensity of the current magnetic field by adjustment of the detecting current. This method changes the direction of the combined magnetization moment of the magnetostatic coupling magnetic field of the pinned magnetic layer and the current magnetic field. A variable range of the detecting current, however, is narrow, and the control of the tilt of the variable magnetization of the free magnetic layer is insufficient.
In the spin-valve thin-film element, as shown in FIG. 22, in which the magnetostatic coupling magnetic field Hp4 of the pinned magnetic layer 30 and the current magnetic field Hi4 of the detecting current i4 are in the same direction (assisting direction), the direction of the variable magnetization Hf10 of the free magnetic layer 50 cannot be readily controlled.
Also in the spin-valve thin-film element, as shown in FIG. 23, in which the magnetostatic coupling magnetic field Hp5 of the pinned magnetic layer 30 and the current magnetic field Hi5 of the detecting current i5 are formed in different directions (counter directions) and the magnetostatic coupling magnetic field Hp5 is larger than the current magnetic field Hi5, the direction of the variable magnetization Hf20 of the free magnetic layer 50 cannot be readily controlled.
Also in the dual spin-valve thin-film element, as shown in FIG. 26, in which the current magnetic fields Hi40 and Hi50 of the detecting currents i40 and i50 affect the variable magnetization Hf40 of the free magnetic layer 45 from opposite directions so that the influences are offset, the direction of the variable magnetization Hf40 of the free magnetic layer 45 cannot be readily controlled.
Accordingly, it is an object of the present invention to provide a spin-valve thin-film element which can readily control the direction of a variable magnetization of a free magnetic layer and which exhibits high heat resistance, high reliability, and small asymmetry.
It is another object of the present invention to provide a thin-film magnetic head provided with the spin-valve thin-film element.
A spin-valve thin-film element in accordance with the present invention comprises a substrate; an antiferromagnetic layer formed on the substrate; a pinned magnetic layer in contact with the antiferromagnetic layer, the direction of the pinned magnetization being pinned by an exchange coupling magnetic field of the pinned magnetic layer and the antiferromagnetic layer; a nonmagnetic conductive layer formed between the pinned magnetic layer and a free magnetic layer; a biasing layer for orientating the direction of a variable magnetization of the free magnetic layer in a direction perpendicular to the direction of the pinned magnetization of the pinned magnetic layer; a conductive layer applying a detecting current to the pinned magnetic layer, the nonmagnetic conductive layer, and the free magnetic layer; a biasing conductive layer for controlling the direction of the variable magnetization of the free magnetic layer; and at least one current applying means for applying a current to the conductive layer and the biasing conductive layer.
While the arrangement of the layers has been described in a preferred manner, they may be operatively connected in other fashions as long as the required electrical, mechanical, and magnetic properties of a spin valve or magnetic head are achieved. They may also have one or more additional layers between any or all of them.
In this spin-valve thin-film element, the current applied to the biasing conductive layer controls the variable magnetization direction of the free magnetic layer. That is, the variable current magnetic field of the biasing conductive layer compensates for a magnetostatic coupling magnetic field of the pinned magnetic layer and a current magnetic field of the detecting current. The magnetostatic coupling magnetic field affects the variable magnetization direction of the free magnetic layer. The variable current magnetic field controls the variable magnetization direction of the free magnetic layer. Thus, the spin-valve thin-film element exhibits high thermal resistance, superior reliability, and small asymmetry. Herein, the asymmetry means the degree of asymmetry of an output waveform. When a waveform shown in FIG. 27 is output, the asymmetry is defined by the following equation:
Asymmetry (%)={(TAA+)xe2x88x92(TAAxe2x88x92)}/{(TAA+)+(TAAxe2x88x92)}xc3x97100
wherein TAA+ is the maximum output voltage at the positive side and TAAxe2x88x92 is the maximum output voltage at the negative side. When the asymmetry reaches zero, the output waveform is highly symmetry.
The asymmetry is zero when the variable magnetization direction of the free magnetic layer is perpendicular to the pinned magnetization direction of the pinned magnetic layer. When the asymmetry is large, information on a recording medium cannot be exactly read out, resulting in errors. Thus, a small asymmetry represents improved reliability of output signal processing and thus a spin-valve thin-film element having a small asymmetry exhibits high read accuracy.
In a preferred embodiment, the spin-valve thin-film element has a dual structure in which the nonmagnetic conductive layer, the pinned magnetic layer, and the antiferromagnetic layer are formed on both sides of the free magnetic layer in the thickness direction.
Since the dual spin-valve thin-film element has two groups of triple layer configurations, each including a free magnetic layer, a nonmagnetic conductive layer, and a pinned magnetic layer, a large rate of change in resistance xcex94MR suitable for high-density recording is obtainable compared to single spin-valve thin-film elements.
Preferably, the current is applied to the biasing conductive layer to form a current magnetic field in a direction opposite to a combined magnetization moment of a magnetostatic coupling magnetic field of the pinned magnetic layer and a current magnetic field of the detecting current. The combined magnetization moment affects the variable magnetization direction of the free magnetic layer. In this configuration, the current magnetic field of the biasing conductive layer is opposite to and compensates for the combined magnetization moment of the magnetostatic coupling magnetic field and the current magnetic field. Thus, the variable magnetization direction of the free magnetic layer can be controlled in a desired direction.
When the direction of a magnetostatic coupling magnetic field of the pinned magnetic layer affecting the variable magnetization of the free magnetic layer is the same as the direction of a current magnetic field of the detecting current affecting the variable magnetization of the free magnetic layer, a current is applied to the biasing conductive layer to form a current magnetic field in a direction opposite to the current magnetic field of the detecting current. In this configuration, the current magnetic field of the biasing conductive layer is opposite to and compensates for the magnetostatic coupling magnetic field of the pinned magnetic layer and the current magnetic field of the detecting current. The magnetostatic coupling magnetic field and the current magnetic field affect the variable magnetization direction of the free magnetic layer. Thus, the variable magnetization direction of the free magnetic layer can be controlled in a desired direction.
Preferably, the current is applied to the biasing conductive layer to form a current magnetic field in a direction opposite to a magnetostatic coupling magnetic field of the pinned magnetic layer, which affects the variable magnetization of the free magnetic layer.
In this configuration, the current magnetic field of the biasing conductive layer is opposite to and compensates for the magnetostatic coupling magnetic field of the pinned magnetic layer, which affects the variable magnetization direction of the free magnetic layer. Thus, the variable magnetization direction of the free magnetic layer can be controlled in a desired direction.
Preferably, the biasing conductive layer is in contact with the antiferromagnetic layer. In this configuration, no additional conductive layer for supplying a current to the biasing conductive layer is necessary. Thus, the spin-valve thin-film element can be readily produced.
Preferably, an insulating layer is formed between the biasing conductive layer and the antiferromagnetic layer. The insulating layer prevents shunt loss in the spin-valve thin-film element.
Preferably, the biasing conductive layer and the conductive layer are connected in series. A current in the conductive layer and a current in the biasing conductive layer can be supplied from only one current supply unit. Thus, the spin-valve thin-film element can be readily formed without providing another current supply unit. However, the at least one current applying means may include two current applying means. The first current applying means connected to the biasing conductive layer. The second current applying means connected to the conductive layer.
In this configuration, the connection between the biasing conductive layer and the current supply unit is applicable to both cases when a current is supplied to the biasing conductive layer. The first case is when a current having the same direction as that of the detecting current is supplied to the biasing conductive layer. The second case is when a current having the opposite direction to that of the detecting current is supplied to the biasing conductive layer. Thus, the direction of the current supplied to the biasing conductive layer can be determined without restriction and regardless of the direction of the detecting current.
Moreover, the intensity of the current in the biasing conductive layer can be controlled without restriction while the intensity of the detecting current is not affected. Thus, tilting of the variable magnetization direction of the free magnetic layer due to the magnetostatic coupling magnetic field of the pinned magnetic layer and the current magnetic field of the detecting current is satisfactorily controlled.
As described in the embodiments of the present invention, the variable current magnetic field controls the variable magnetization direction of the free magnetic layer. The variable current magnetic field has a variable direction to compensate for the variable magnetization direction. In operation, the variable direction varies to compensate for changes in the variable magnetization direction. A thin-film magnetic head in accordance with the present invention comprises the above-mentioned spin-valve thin-film element. The thin-film magnetic head exhibits high thermal resistance, superior reliability, and small asymmetry.